Conventionally, in a halogen lamp for business machine, a mercury lamp for a liquid crystal projector light source, or a metal halide lamp for general lighting, etc., an internal lead and an external lead are joined together through a metallic foil in a sealing portion, so as to secure airtightness of a light emission space in the lamp tube. When such internal and external leads were conventionally joined to the metallic foil, for example, a joint portion of the metallic foil and the internal lead of the halogen lamp for business machine, which is currently sealed by pinch sealing, or a joint portion of the metallic foil and the internal lead of a mercury lamp for a projector light source, which is currently sealed by shrink-sealing, was joined by a resistor welding.
However, in such a resistor welding process, the welding conditions change due to changes of a welding electrode rod with passage of time, so that the welding quality is not stabilized, whereby there is a problem of peeling due to insufficient adhesive strength or a problem of generation of holes in the metallic foil at time of the welding. Furthermore, in the resistance welding process, application of pressure is necessary at the time of welding in order to obtain the welding strength, so that there is a possibility that deformation and creasing of detailed parts, such as the electrode or the lead rod may occur by the pressurization.
Japanese Laid Open Patent No. 2004-363014 teaches a tungsten electrode and a molybdenum foil are joined by a laser welding using a YAG laser in manufacture of a high-pressure discharge lamp, instead of the resistance welding. Also, refer to Japanese Laid Open Patent No. 2003-257373.